Long term objective of this research is the quantitative description of the placental exchange of metabolites between mother and fetus. Attention will be focused on the regulation of maternal placental blood flow and the uptake of metabolic substrates by the pregnant uterus. The experiments will be on nonanesthetized, unstressed sheep with indwelling catheters in the left ventricle, the femoral arteries, the uterine veins and the amniotic cavity. Electromagnetic flow probes around both uterine arteries and radioactive microspheres will be used as methods of flow measurement. The growth of placental blood flow in single and twin pregnancies will be described and related to placental and fetal growth. Uterine uptakes of 02, glucose, amino acids in starved ewes will be compared with normal values.